Devices for the automated release of liquid medicaments are normally used with patients who have a continuous variable need of a medicine that can be administered by subcutaneous infusion. Specific applications are, for example, certain pain therapies and the treatment of diabetes, in which computer controlled infusion pump devices are used, such as insulin pumps. Such devices can be carried by a patient on the body, and contain a certain amount of liquid medicament in a reservoir in the form of a container. The medicine reservoir often comprises medicine sufficient for one or more days. The liquid medicament is supplied to the patient's body from the reservoir by subcutaneous infusion of injection, through an infusion cannula or an injection needle.
In self-administration of liquid medicaments, such as the self-administration of insulin, the patients administering by means of an infusion pump are increasingly emphasizing convenience and discretion. As a consequence such infusion devices are designed to be small to increase discretion and improve patient comfort.
While there are fully or partly disposable single-use infusion pump devices, such devices are typically non-disposable and are loaded with a disposable drug cartridge. Disposable cartridges are preferable for sterility and contamination prevention reasons. They may be delivered pre-filled with a certain liquid medicament, or empty, which are self-filled by a user. The self-filled containers may be filled with medicaments that are not available in pre-filled containers. For example, some medicaments have limited availability in pre-filled containers due to a lack of stability in liquid form when stored in plastic containers.
One common type of infusion pump device that is carried on or near the body has a medicine reservoir with a cylindrical ampoule and a displacement piston, which is pushed into the ampoule by a piston rod or threaded spindle in order to convey the liquid medicament. These known designs have the disadvantage of being longer and/or thicker than desired.
Manufacturers may meet the demand for small infusion pump devices in various ways. For example, the cylindrical ampoule may be replaced by a container with a rectangular or another suitable cross-section that interacts with a displacement piston of a corresponding shape. Embodiments of such small infusion pump devices are shown in WO 2008/122135 A1.
A further approach to meet the demand for small infusion pump devices may include replacing a syringe-type dosing mechanism, in which a piston is displaced along a long container axis by an actuator in order to convey an appropriate amount of liquid medicine, with a downstream pump system. In a downstream pump system device a miniaturized pump is arranged downstream of the reservoir and causes a suction pressure that conveys the liquid medicine from the reservoir to its destination. An example for such a pump is described in WO 2004/009162 A1.
The reservoir for a downstream pump system may be a flexible container. Such a flexible container may comprise, for example, two flexible wall sheets that are sealed together. Flexible containers have the advantage of a smaller volume surplus of the container in relation to its content, which reduces the manufacture costs and the achievable dimensions of an infusion pump device using such a flexible container. The volume of some flexible containers may be up to about 10 ml, for example. Medication for diabetes therapy is commonly available in volumes of about 1.5 ml to about 3.5 ml. Other types of therapies, e.g. pain therapy, may require other administration regimes. Therefore, other volume ranges may be more common.
One known problem with flexible containers is residual air within the container. For example, a flexible self-filled container may be provided empty and manually filled with an appropriate liquid medicament. After the flexible container is filled, residual air may persist in the flexible container. If the residual air remains in the container or in the fluidic system of a pump system, it may be administered in place of the liquid medicament, which leads to potentially dangerous dosing errors. Furthermore, the administration of air into a patient's body should generally be avoided for medical reasons.
Yet another issue with residual air present in the fluidic system of an infusion pump device is the reduced stiffness of the fluidic system. Due to the high compressibility of gases such as air in relation to liquids such as water, it becomes difficult to measure the exact pressure in the fluidic system. This impedes the detection of blockages or occlusions in the fluidic system of an infusion pump device by measuring the fluidic pressure.
Known may help a user to fill a container for infusion pump systems. However, the known devices are for use with syringe/ampoule type infusion pump systems, and cannot be properly used with flexible containers. Such filling devices are disclosed, among others, in EP 1952837 A1 and EP 1820485 A1.